1. Chapter 18 The Geography of Soils
Geosystems 5e
An Introduction to Physical Geography
Robert W. Christopherson
Charlie Thomsen

2. The Geography of Soils Soil Characteristics Soil Properties
Color, texture, structure, chemistry
Soil Properties  
Mineral fraction, organic matter, porosity (gases, soil moisture)
Soil Formation Factors
Clorpt  
Soil Classification  
Podzolization, calcification, laterization, salinization
Soil orders: Oxisol/Ultisol; mollisol, spodosol, aridisol, histisol
Know soil horizons (O, A, B, C, R)

3. Soil Sampling and Mapping Units
Figure 18.1

4. Laterization l
Soil Orders:
Oxisols: Amazon region
Ultisols: SE USA

5. Oxisols Oxisols are deeply weathered. Precipitation >> PET
Soluble minerals weathered from A horizon
A horizon can be more than 10-m deep
A horizon characterized by iron and
aluminum oxides, often in high enough
concentration to be commercial ores
Results in reddish to yellow color
Little CEC
Low in fertitlity
Wet tropical areas
Amazon rain forest classic example
Ultisols are similar, characteristic of sub-
tropical areas such as SE USA

6. Oxisols being used for building materials in India

7. Calcification Potential ET about the same as precipitation
Large amounts of organic matter
in O and A horizons, dark color
Get carbonate deposition in B horizon
Very fertile soils if add water
Mollisols characteristic soil order

8. Mollisol Dark O horizon above the 1 Dark A horizon between 1 and 2
-these indicate lots of organic matter
B horizon below the 2
-the white particles are carbonate
nodules
Calcification regime
-ppt about equal to ET
Great plains area
Figure 18.2

9. Podzolization Cool climates Precip > PET Forested areas generally
Strongly leached
Acidic soils
Low CEC and low fertility
Generally an E or spodic horizon
of leached/bleached gray/white
Large surface humus layer
Iron and Aluminum in B horizon
Poor farming areas
NE US

10. Spodosols Cold, forested, moist regimes -NE USA
-Boreal forests worldwide
Lack humus and clay in the A-horion
-A horizon heavily leached
-whiteish colorad from 0 to 0.9
Iron and aluminum oxides in B horizon
-reddish color above and below 2
Low CEC
Infertile soils
Acidic soil waters

11. Salinization Accumulation of salts in arid areas
PET >> precpitation
Aridisols dominant soil order

12. Aridisols PET >> Precipitation Desert soils
Pale, light color near surface
Long periods of soil moisture deficit
Little if any organic matter
High CEC
Very fertile if add water
Salinization is common
Here the white color is from salts that have
precipitated in the soil

13. Kesterson Reservoir
The Kesterson Reservoir in the San Joaquin Valley of California is the recipient of water drained from agricultural fields. Studies of the freshwater wetlands at Kesterson have shown that the water entering Kesterson has brought with it boron, selenium and other trace elements. These material have accumulated to toxic levels in plant and animal communities.

15. Histosols: poorly-drained areas, high OM, wetlands and peat areas

17. Soil Properties Soil Color Soil Texture Soil Structure Soil Chemistry
Soil Acidity and Alkalinity  
Soil nutrients

18. Munsell Soil Color Chart
Figure 18.3

19. Soil Texture Triangle
Figure 18.4

20. Types of Soil Structure
Figure 18.5

21. Soil Colloids and CEC
Figure 18.6

22. pH Scale
Figure 18.7

23. Geophagy People around the world eat clay, dirt or other pieces of
the lithosphere for a variety of reasons. Commonly, it is
a traditional cultural activity which takes place during
pregnancy, religious ceremonies, or as a remedy for
disease. Most people who eat dirt live in Central Africa
and the Southern United States. While it is a cultural
practice, it also fills a physiological need for nutrients.
And of course, kids all over the world still eat dirt.